1. Field of the Invention
The invention relates to threaded fluid ports in base-mounted valves and other equipment which are intended to receive pipes, fittings, plugs or other connecting hardware in a manner such that a fluid-tight joint is formed. The invention is also applicable to ports for electrical conduits or other threaded connections.
2. Description of the Prior Art
Ordinarily, female port threads are formed so as to be compatible with any one of three standard thread forms, known as National Pipe Thread (NPT), British Standard Pipe, Tapered (BSP Tr.), and British Standard Pipe Parallel (BSP Pl.). Often however, it is desired that an available part with a female port thread of one type be fitted with hardware having an external thread of another type. This has heretofore been unfeasible in certain instances. For example, a BSP port thread cannot ordinarily accept NPT hardware without excessive plastic deformation of the mating parts.
It has been common to insert a tapered male thread into a parallel female thread so that sealing is effected only at the outer threads. Here again, however, the use of NPT external threads in a BSP parallel port has not been uniformly satisfactory because of excessive plastic deformation.